Effect of particle size on spin glass state and Curie temperature in Sm0.5Ca0.5MnO3 with charge ordering

The particle size and magnetic properties of charge-ordered (CO) Sm0.5Ca0.5MnO3 (SCMO) manganites prepared by solid-state reaction with ball milling have been investigated. Studies on surface morphology and particle size show that the particle size of SCMO manganite without ball milling is relative large (about 4 mu m). With the ball milling, the particles begin to disperse, the particle size gradually decreases, and it reaches hundreds to tens of nanometers after milling for 12 h to 36 h. At this time, the particles agglomerate. Magnetization versus temperature (M-T) measurements and the inverse susceptibility versus temperature (chi(-1)-T) measurements show ferromagnetic (FM) transition at Curie temperature (T-C) and spin glass (SG) state at freezing temperature (T-f). Moreover, there is a bulging (sunken) peak near 273 K in the M-T (chi(-1)-T) curves, suggesting that the CO anti-ferromagnetic (AFM) phase appears in the SCMO. The temperature corresponding to this bulging (sunken) peak represents CO temperature (T-CO). The results of magnetization versus field (M-H) loops, M-T curves and chi(-1)-T curves show that the decrease of particle size with ball milling can suppress the formation of CO-AFM phase, decreasing the T-f, T-C, T-CO and coercive field (H-C). Our work shows that it is a way to tune SG state and Curie temperature by controlling the particle size of the manganites with charge ordering.